Hydraulic control means for roller mills and the like



Oct. 21, 1958 E; BQSSHARD 4 2,355,900

' HYDRAULIC CONTROL MEANS FOR ROLLER MILLS AND THE LIKE Filed Nov. 20, 1956 Fig.1

United States Patent HYDRAULIC CONTROL MEANS FOR ROLLER MILLS AND THE LIKE Ernst Bosshard, Steinacker, Uzwil, Switzerland, assignor to Gebrueder Buehler, Uzwil, Switzerland, a Swiss firm Application November 20, 1956, Serial No. 623,431

Claims priority, application Switzerland November 26, 1955 2 Claims. (Cl. 121-38) For regulating the forces in grinding roller-mills, hydraulic means are used on account of their easy adjustability. Two types of hydraulic systems are known in the art, namely, the hydrostatic system and the hydrodynamic system which latter comprises a continuously feeding pump. The hydrostatic system is of simple construction, but the forces vary even in response to slight temperature changes, and thus the operator has to pay continuous and full attention to the grinding mill. The hydrodynamic system is somewhat more complicated but has the great advantage that the pressure set on a pressure-regulating or control valve remains constant without any special supervision. However, in spite of this important advantage, the hydrodynamic system has not been used to any appreciable extent since it only permits increases but no decreases in force without first reversing the pressure to zero.

The present invention provides means to avoid such disadvantages of the hydrodynamic system and relates to a device for hydraulically regulating or controlling a bearing pressure, for example, in connection with roller mills, with the aid of a continuously feeding pump, a check valve being inserted in the line from a control valve to a pressure-generating cylinder. The novel device is characterized by the provision of a free passage of small cross-sectional area between the two sides of the check valve.

A preferred embodiment of the invention and two examples of its application are shown in the accompanying drawing, in which Fig. 1 shows the hydrodynamic system and one form of its application, a pressure-control valve and two check valves being illustrated in section drawn to a much larger scale than the other components, and Fig. 2 depicts another form of application of the system shown in Fig. l.

A continuously feeding pump 1 supplies oil from a tank 3 through a line 2 into a relief valve 4 which communicates with tank 3 via a return line 5. From valve 4 the oil passes through a line 7 to a four-way valve 8. In the position of an operating lever 9 shown in solid lines, line 7 is connected to a pressure-control valve 11 of known construction through a line 10, and a line 12 from the release side of a double-acting piston 13 moving in a cylinder 14 is connected via valve 8 to a line 15 leading to tank 3. When moving lever 9 into the position 9 shown in broken lines, lines 7 and 12 on one hand, and and on the other hand are interconnected.

Line 10 leads into an inlet chamber 16 in the casing of valve 11, and this chamber 16 communicates with an outlet chamber 18 via a bore 17. A line 20 leads from chamber 18 via a check valve 21 to the pressure side of piston 13 which, through its rod 13a, transmits the generated bearing pressure to the element to be regulated, for example, to a movable roller MR coacting with a fixed roller FR, or to a grinding bar 51 (Fig. 2) coacting with a roller R. Valve 21 is necessary to prevent the 2,856,900 Patented Oct. 21, 1958 transmission of any possible surges in valve 11 to piston 13.

The casing of valve 11 serves as cylinder for a piston 23 which latter has two heads 24 and 25 of the same diameter as bore 17, said heads being interconnected by a rod 26 of smaller diameter. Head 24 is loaded by a spring 28 and is subjected to the pressure in an equalizing chamber 29'. When piston 23 moves against the action of spring 28, head 25 can fill'entirely and thus closes the bore 17. Head 25 is provided with bores 31 and 32 of relatively large diameters in order to positively subject its bottom side to the pressure in chamber 18. Bore 32 communicates with chamber 29 via a bore 33 of small diameter, and the pressure in chamber 29 is controlled by a relief valve 36 which normally closes a bore 35 communicating with chamber 29. The ball, of valve 36 is loaded by a spring 37 whose force may be adjusted which is provided with a notch or flute 43 of small cross sectional area so as to aiford a free passage between the two sides of the valve 21.

A line 45, which branches off from line 20, extends from the pressure side of piston 13 via a second check valve 46, with piston 47 under pressure by spring 48, to high-pressure chamber 16 of control valve 11.

The novel hydrodynamic system operates as follows. Operating lever 9 is in the position shown in solid lines, and roller MR (Fig. 1) or grinding bar 51 (Fig. 2) is held under pressure by piston 13. In order to increase the load or hearing pressure, screw 38 is slightly tightened to raise the response pressure of valve 36. The resulting higher pressure in outlet chamber 18 is transmitted through check valve 21 to the pressure side of piston 13. When the pressure in outlet chamber 18 exceeds the response pressure of valve 36, the latter opens and a portion of the oil in equalizing chamber 29 is returned through line 39 back into tank 3. The pressure in chamber 29 drops, and piston 23 moves against the action of spring 28 since bore 33 is of relatively small cross-section. The free cross-section at the point of throttling between bore 17 and slide-valve head 25 decreases.

In operation, there is a steady, slight return flow of oil through bore 33, equalizing chamber 29, bore 35, valve 36 and line 39 into tank 3, as indicated by the double-tipped broken-line arrows. Due to this slight, continuous return flow, the pressure remains at its set value.

In order to decrease the bearing pressure exerted by piston 13, screw 38 is slightly loosened to decrease the responsive pressure of valve 36 and the pressure in outlet chamber 18. Due to the provision of groove 43 in the body 42 of valve 21, such pressure decrease is transmitted to the pressure side of piston 13.

When a harder fragment is being ground, check valve 21 prevents the roller MR (Fig. 1) or grinding bar 51 (Fig, 2) from striking back. The desired pressure is gradually built up through groove 43.

When a foreign body is passing between the grinding elements, i. e. between the rollers MR and FR or between the roller R and the grinding bar 51, and the pressure increases to between a value above that of the pressure generated by pump 1 in the chamber 16, the oil can flow back through the check valve 46. Thus this check valve 46 is also a safety device and prevents the build-up of undesirably high pressure. After the passing of the foreign body, the grinding elements return into engaging position.

In order to release roller MR or grinding bar 51, operating lever 9 is swung into position 9', whereby the lines 7 and 12 are interconnected, and the oil under pressure flows to the opposing side of piston 13. The oil on the pressure side of piston 13 then flows back into tank 3 through lines 20 and 45, check valve 46, highpressure chamber 16, line 10, four-way valve 8 and return line 15, as indicated by the single-tip broken-line arrows.

The flow of oil to the pressure side of piston 13 is indicated in Fig. l by arrows shown in solid lines.

The arrangement shown and described is particularly suited in cases when several control valves 11 are connected with a single relief. valve 4.

This arrangement permits gradual increase or reduction of the bearing pressure and also afiords a positive disengagement ofthe bearing pressure.

What I claim as new and desire to secure by Letters Patent, is:

1. In a hydrodynamic system comprising a source of constant pressure, at least one pressure control valve connected to said source of constant pressure, adjustable means associated With said pressure control valve for providing a controlled return flow of a fluid under pressure therefrom, a hydraulic cylinder, a piston in said cylinder, a first check valve and a second check valve between said cylinder at one side of said piston and said pressure control valve, said first check valve operating in a sense toward said cylinder and said second check valve operating in a sense opposed to that of said first check valve, the improvement which consists in that said first check valve has a relatively small passage for return flow of fluid under pressure from said cylinder to said pressure control valve.

2. The structure according to claim 1, wherein a plurality of pressure control valves are connected to said source of constant pressure.

References Cited in the file of this patent UNITED STATES PATENTS 577,489 Mills Feb. 23, 1897 1,972,462 Schafer Sept. 4, 1934 2,293,118 Cumming Aug. 18, 1942 2,460,774 Trautman Feb. 1, 1 949 2,735,404 Komph Feb. 21, 1,956 2,784,729 Schofiel Mar. 12, 19-57 FOREIGN PATENTS 506,355 Great Britain May 26, 1 939 

